Antenna



C. F. LYLE Jan. 21, 1958 ANTENNA Filed Jan. 17, 1955 gill!!! UnitedStates 2,820,964 Patented Jan. 21, 1958 tice ANTENNA Charles F. Lyle,Morris Plains, N. J., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationJanuary 17, 1955, Serial No. 482,005 11 Claims. (Cl. 343-708) Thisinvention relates to antenna systems and more particularly to an antennasystem for use on an aircraft.

The principal object of the invention is to provide an isotropic fieldpattern in an airborne antenna system. Other objects are to reduce airturbulence and drag, increase the safety and the operating eiiiciency,and simplify the mechanical construction of such an antenna.

It is desirable that an airborne antenna system have a coverage patternwhich is uniform in all directions so that the aircraft can communicatewith other aircraft or ground stations, whatever the relative position.The antenna systems at present found on aircraft are not entirelysatisfactory in operation for a number of reasons. Due to the locationof the antenna, the reflection and shadow effects caused by the aircraftframe are too great. It is an established fact that in the antennasystems now used for ultra-high-frequency communication the signal isoften blanked out by the aircraft frame during the critical periods whenthe control tower is attempting to give instructions to the approachingaircraft, or when the aircraft is attempting to communicate with anothernearby aircraft. Also, standing Waves set up on the surface of theaircraft frame not only distort the field pattern but may give rise toradio-frequency voltages of suicient magnitude to ignite the fuel in ajet plane. Some types of antennas create air turbulence and air-drag,are located too far from the radio transmitter or receiver, or aredilicult to manufacture and maintain.

The antenna system in accordance with the present invention overcomesthese and other disadvantages. The antenna is mounted on a tube whichextends forwardly from the nose of the aircraft, thus greatly reducingthe blanking effects heretofore encountered when negotiating a landingor when communicating with a nearby aircraft. Many jet-propelled planesnormally have a ram tube which may be used for this purpose. The antennacomprises a pair of oppositely disposed, quarter-wave, dipole elementsinsulatingly secured at their bases to the tube. The elements arepreferably bent and of streamlined cross section to reduce drag andturbulence. The ends of the elements may be beveled for the same reason.The antenna is spaced at least three wavelengths from the base of theram tube in order to provide a substantially isotropic eld pattern.Also, this distance is preferably made an integral number of halfwavelengths in order to prevent the formation of standing waves on theouter or inner surfaces of the aircraft. Electrical connection betweenthe antenna and the associated radio receiver or transmitter may be madeby means of a transmission line, preferably of the coaxial type,positioned within the tube. The outer conductor of the coaxial line maybe grounded to the ram tube at a point a quarter wavelength from theantenna in order to provide a matching termination and thereby increasethe operating elciency.

The nature of the invention and its various objects, features, andadvantages will appear more fully in the following detailed descriptionof a typical embodiment illustrated in the single ligure of theaccompanying drawing.

A metal ram tube 1 is shown extending in the forward direction from thenose 2 of a jet-propelled airplane. The base of the tube 1 is securelyfastened to a dividing island 3 which is vertically positioned at thecenter of the open nose of the plane which serves as the air intakeorifice for the jet engine. The ram tube 1 may be considerably longerthan shown, is preferably tapered, and may have a pitot tube or otherdevices mounted at its forward end. A pair of oppositely disposed dipoleelements 4 and 5 are secured at their bases to the insulators 7 and 8,respectively, which are inserted in holes cut in the wall of the tube 1.

Each of the elements 4 and 5 has a length approximately equal to aquarter wavelength at the midband frequency fM of the operating band,has a cross section which is diamond shaped, as shown, or is otherwisestreamlined, and has a beveled end as shown at 9. The elements arepreferably bent at a right angle to reduce drag and Widen the operatingband. They may be bent to the rear, as shown, or in the oppositedirection. In order to prevent the formation of standing radio-frequencywaves on the outer or inner surface of the aircraft frame, the antenna 45 is located an integral number of half wavelengths from the dividingisland 3. That is, the distance D is made equal to an integral number ofhalf wavelengths at fM. The elimination of external standing wavesgreatly increases the uniformity of the radiation pattern. Eliminatinginternal standing waves avoids the possibility of prematurely ignitingthe fuel and causing a serious accident. Also, the distance D ispreferably made at least three wavelengths at the frequency fM in orderto reduce the shadowing effect to the rear caused by the aircraft frame,thus making the coverage pattern more nearly isotropic.

The antenna 4-5 is connected to the radio transmitter or receiver, notshown, by a comparatively short coaxial transmission line 10 which runsalong the inside of the tube 1 and is held in place by supports such as11 and 12. The inner conductor 13 of the line 10 is connected to thedipole element 4. The outer conductor 14 is connected to the element 5by a connector 15. The support 12 is made of metal and serves to groundthe outer conductor 14 to the tube 1. The distance S between the support12 and the elements 4, 5 is made a quarter wavelength at the frequencyfM to provide a matching termination for the line 10, thus avoidingreflection of energy and improving the operating eficiency.

It is to be understood that the above-described arrangement isillustrative of the application of the principles of the invention.Numerous other arrangements may be `devised by those skilled in the artwithout departing from the spirit and scope of the invention.

What is claimed is:

l. In a jet-propelled airplane having an air intake orice in the nosethereof and a dividing island positioned in said orifice, an antennasystem comprising a ram tube securely fastened at one end to saiddividing island to project in the forward direction, a pair ofoppositely disposed, quarter-wave, dipole elements insulatingly securedat their bases to said tube at a distance from said one end, and atransmission line positioned within said tube and electrically connectedto said elements.

2. A system in accordance with claim 1 in Which said distance is equalto an integral number of half wavelengths.

3. A system in accordance with claim 1 in which said distance is equalto at least three wavelengths.

4. A system in accordance with claim 1 in which said transmission lineis of the coaxial type, and means for asaoea conductively `connectingthe outer conductor of said line to said tube at a pointspaced aquarterrwavelength from said elements.

5v. A systremrin accordance' with claim l inwhich each of said elementsis'be'nt in the backward direction at a right angle. Y l

-6, Asystem in accordance with claim 1 inlwhich each of-said elementsvisbentat a right angle. Y y

7.--A-system in accordance with "c1aim`6 in which the outer endfofearchof said elements istbeveled.

8. Arsystem'in accordance with claim 6 in which each of '-saidelementshas a diamondlshaped cross section and a 'beveled onte'r end.

9. Asystemin accordance withvclaim 2 in which said distance is equaltoatleast three wavelengths.

`L10. An antenna system for an aircraft comprising a tapered tubeadapted for mounting at its larger end on the nose of the aircraft toextend in the forward direction,

"aipairofroppositely disposed, Vquarter-wave, dipole elementsinsulatingly secured at their bases to saidk tube at a distance fromsaid larger end equal to an integral number of half wavelengths andequal to at least three wavelengths, and a transmission line positionedWithin said tube and electrically connected to said elements, saidelements being bent in a backward direction at a right angle and havinga streamlinedxcross section and beveled ends.

11. A system in accordance with claim 10 in Vwhich said ReferencesCited-in the tile of this patent UNITED STATES PATENTS Cork Apr. 4, 1939Peterson Aug.'9, 1949

